I loose power when exclerating up a hill or onto a freeway.

Light on? Have a scan test and check cat. converter. Also fuel pressure.

Agree with wetry and is it running hot at all? How many miles on engine?

also u could repl fuel filter and see if that helps.

With the work done already, I agree the most likely cause is the catalytic converter needing replacement. Exhaust is not flowing out properly causing the loss of power and the engine to choke itself under higher performance conditions.